1. Field of the Invention
The present invention generally relates to plastic wheel covers for a vehicle wheel. More particularly, this invention relates to bolt-on wheel covers that are integrally retained to, but thermally isolated from, lug nuts of a vehicle wheel.
2. Description of the Prior Art
Wheel covers have been used on vehicle wheels for many decades for purposes of aesthetic design, reduction in drag coefficient, and for improvement of brake cooling. Wheel covers have been fastened to wheels with a variety of devices including clips, springs, and integral retaining features. In addition, traditional materials for forming wheel covers include steel and aluminum. Plastic, however, has increasingly been used in order to reduce cost and weight, and to increase design flexibility.
Use of “high-temperature” plastic for vehicle wheel covers is well known in the art. In contrast, use of “low-temperature” plastic is less known, but is becoming more popular because it can be chrome plated for aesthetic value. A popular technique for retaining a wheel cover to the wheel involves connecting the wheel cover to the lug nuts of the wheel. The lug nuts, however, tend to be prohibitively hot due to heat transfer generated from a brake component to which the lug nuts are indirectly connected. Under severe conditions, brake lining temperatures are known to exceed 1000° F. while wheel temperatures are known to exceed 500° F. Therefore, care must be taken not to subject the low-temperature cover to the hot lug nuts of the wheel. Accordingly, there are several different wheel covers having various lug nut retention devices to select from, that could be described as: cap retained, bolt-on, integral press-on, and retainer press-on wheel covers.
Cap retained covers involve a cover body that mounts to the wheel and includes lug towers that loosely circumscribe the lug nut or stud. A separate cap retainer interlockingly engages the lug nut or stud to sandwich an apical shoulder of the lug tower between the retainer and the wheel. Several examples include: U.S. Pat. No. 4,895,415 to Stay et al., U.S. Pat. No. 4,998,780 to Eshler, U.S. Pat. No. 5,181,767 to Hudgins et al., U.S. Pat. No. 5,667,281 to Ladouceur, and U.S. Pat. No. 5,842,749 to DiMarco. With some of these designs, the cover is spaced away from the wheel by the cap retainer. These designs, however, require use of several cap retainers thus adding to part count and assembly steps—thus increasing costs. Additionally, the cap retainers have been known to work loose and fall off, thereby resulting in loss of or damage to the wheel cover itself. Finally, the retainers have been known to slacken due to temperature creep, resulting in a slack condition between the cover and the wheel. This slack condition also results in noise generated by the loose wheel cover rattling against the wheel.
Bolt-on covers involve a cover body having open lug towers for mounting over lug studs on a wheel. Subsequently, a lug nut mounts to the lug stud to trap an apical shoulder of the lug tower therebetween. An example of this is illustrated in U.S. Pat. No. 5,520,445 to Toth. Here the apical shoulder of the lug tower comes in direct contact with the hot lug nut. In another embodiment, a skirt on the lug nut spaces the cover away from the lug nut. The skirt, however, is taught as a device for retaining the lug nut to the cover for disassembly purposes, and not for thermal isolating purposes. In fact, such skirts are typically metallic and therefore there is no reason to believe that the skirt provides any thermal insulation at all.
Integral press-on wheel covers typically involve a cover body provided with integral tubular extensions, or lug towers, each having an integral projection for engaging a shoulder of a lug nut. Several examples include: U.S. Pat. No. 4,382,635 to Brown et al., U.S. Pat. No. 4,707,035 to Kondo et al., U.S. Pat. No. 5,071,197 to Webster et al., and U.S. Pat. No. 5,163,739 to Stanlake. With this configuration, the wheel cover is aligned to the wheel and pressed thereto such that each lug tower expands open over each lug nut shoulder and snaps shut behind each shoulder to retain the cover to the wheel. Unfortunately, traditional integral press-on covers come in direct contact with the hot lug nuts and therefore necessitate use of only non-platable high-temperature plastic.
Finally, retainer press-on covers involve a cover body including lug towers each having an intermediate retainer therein for gripping a lug nut. For example, U.S. Pat. No. 4,842,339 to Roulinson addresses the problem of having to use a non-standard lug nut having a special bulge for engaging the wheel cover. Roulinson teaches use of an expandable ring within each lug tower for gripping a standard lug nut. Unfortunately, the expanding ring is metal and therefore conducts heat from the lug nut to the cover. In addition, the expanding ring is an extra part that adds part count and assembly time, thereby increasing costs.
Another example, as set forth in U.S. Pat. No. 5,249,845 to Dubost, is directed to the problem of difficulty in removing wheel covers from a wheel for servicing purposes. Dubost teaches use of an intermediate sliding sleeve retainer within each lug tower for a more compliant grip on the lug nut. Unfortunately, the sleeve adds to part count and assembly time, thereby increasing costs. In addition, the Dubost design involves moving parts instead of a more robust static state design. Further, Dubost does not teach use of a thermally insulating plastic for the sleeve.
Lastly, U.S. Pat. No. 5,297,854 to Nielsen et al., involves a plastic cover body having lug towers with tulip retainers fastened thereto for gripping the lug nuts. The tulip retainers expand open over the lug nut and collapse behind a shoulder on the lug nut for retention thereto. Also, Nielsen et al. is directed to the problem of poor grip of integral press-on architecture and does not teach thermal isolation of the cover body from hot wheel lugs. Unfortunately, each tulip retainer must be assembled to the cover body, thereby adding unwanted assembly time and expense. Additionally, Nielsen et al. appears to be applicable to only hub-style wheel covers and not full face style wheel covers. Full face style wheel covers are highly desirable and ordinarily require a more positive retention method, like the bolt-on retention configuration, to resist continual tension on the retaining area of the cover created by pre-load across the face of the cover. In addition, the Nielsen et al. retaining method is more susceptible to theft of the cover than the bolt-on configuration. Finally, Nielsen et al. also does not apply to a cover with open lug towers that permit display of decorative lug nuts.
Therefore, what is needed is a plastic wheel cover that overcomes the shortcomings of the prior art. Firstly, the cover should be primarily composed of chrome platable “low-temperature” plastic that is thermally isolated from the lug nuts. Secondly, the cover should have integral isolators that serve to isolate the cover from the lug nuts and that are easily assembled or are easily molded in place. Thirdly, the cover should include a robust retaining architecture to permit use of full-face wheel covers, enable open lug towers for display of decorative lug nuts, and provide better theft deterrence.